Proprotein convertase subtilisin/kexin type 9a (PCSK9) is a member of the proteinase K subfamily of subtilases. The PCSK9 gene (NARC-1) has been identified as a third locus involved in autosomal dominant hypercholesterolemia (ADH), characterised by high levels of low-density lipoprotein (LDL), xhantomas, and a high frequency of coronary heart disease. The other two loci being apolipoprotein-B (Apo-B) and the LDL receptor (LDLR). PCSK9 act as a natural inhibitor of the LDL-receptor pathway, and both genes are regulated by depletion of cholesterol cell content and statins via sterol regulatory element-binding protein (SREBP). PCSK9 mRNA and protein levels are regulated by food intake, insulin and cell cholesterol levels (Costet et al., J. Biol. Chem. January 2006).
The human NARC1 mRNA (cDNA) sequence, which encodes human PCSK9 is shown as SEQ ID NO: 5 (NCBI Acc. No. NM—174936).
The human PCSK9 polypeptide sequence (nascent) is NCBI Acc. No. NP—777596. The polypeptide has a signal peptide between residues 1-30, which is co-translationally cleaved to produce a proprotein (amino acids 31-692), which is subsequently cleaved by a protease to produce a mature protein corresponding to amino acids 83-692. A glycosylation site has been characterised at residue 533.
Park et al., (J. Biol. Chem. 279, pp 50630-50638, 2004) discloses that over-expression of PCSK9 reduced LDLR protein resulting in an increase in plasma LDL cholesterol, and suggests that an inhibitor of PCSK9 function may increase LDLR protein levels and enhance LDL clearance from plasma.
Rashid et al., (2005, PNAS 102, No 15, pp 5374-5379) discloses that knockout mice lacking PCSK9 manifest increased LDLR protein leading to an increased clearance of circulating lipoproteins and decreased plasma cholesterol levels, and suggests that inhibitors of PCSK9 may be useful for the treatment of hypercholesterolemia and that there may be synergy between inhibitors of PCSK9 and statins to enhance LDLRs and reduce plasma cholesterol.
WO01/57081 discloses the NARC-1 polynucleotide sequence and discloses that antisense nucleic acids can be designed using the NARC-1 polynucleotide sequence, and that such antisense nucleic acids may comprise modified nucleotides or bases, such as peptide nucleic acids.
WO2004/097047, which discloses two mutants of PCSK9 which are associated with ADH, suggests that antisense or RNAi of such PCSK9 mutants may be used for treatment of ADH.
The mainstay of atherosclerotic pharmacotherapy has been chronic therapy to prevent or slow the development of atherosclerotic plaques primarily by focusing on lowering LDL or “bad cholesterol” as a therapeutic endpoint. Statin therapy, for example, has greatly contributed to improved cardiovascular health; however, adverse effects such as rhabdomyolysis, remain an impediment. Furthermore, statins do little in an acute situation, for example, to reduce vulnerable, unstable atherosclerotic plaque during an ischemic episode. Acute treatment has largely relied on thrombolytics (such as tPA) and surgical intervention such a percutaneous transluminal coronary angioplasty (PTCA) and coronary artery bypass graft (CABG). While thrombolytics provide relief by decreasing or eliminating an occluding thrombus, they do not alter the underlying pathology. Interventions such as PTCA carry their own risks and are often unsuitable for patients in acute conditions. Hence current pharmacologic therapies do little to help patients once unstable plaque presents as a risk. (See, Newton and Krause 2002, Atherosclerosis S3:31-38).
Yet despite the improved understanding of the pathophysiology of myocardial infarction and developments in atherosclerotic pharmacotherapy, safe and effective treatment modalities which have a fast onset of action to allow for treatment in the acute phase, and which do not have serious side effects when used for long term treatment are still desired.
The compounds of the present invention are potent and non-toxic inhibitors of PCSK9, useful for in treatment of hypercholesterolemia and related disorders.